Spark plug, insulating material therefor, and method of making the same



0. C. ROHDE Nov. 15, 1938.

SPARK PLUG, INSULATING MATERIAL THEREFOR, AND METHOD OF MAI (1N1 THL SAME Filed April 22, 1937 F i E13- iii Patented Nov. 15, 1938 UNITED STATES SPARK PLUG,

INSULATING MATERIAL THEREFOR, AND METHOD OF MAKING THE SAME Otto C. Rohde, Toledo,

Ohio, assignor to Champion Spark Plug Company, Toledo, Ohio, a corporation of Delaware Application 19 Claim.

This application is a continuation in part of my prior application for Spark plug, filed February 13, 1936, Serial No. 63,752.

This invention relates to a spark plug, and more particularly to a spark plug having a shell and a central electrode and powder compacted between the shell and electrode to form a seal, a holding means securing the parts in relative position, and insulation.

The invention further relates to an electric insulating material which is characterized by a high dielectric in combination with a relatively high conductivity of heat. The material is also impervious to gas and has a relatively high degree of elasticity for material which is thus impervious.

The invention further relates to a method of producing the insulating material.

Details of the invention will appear as the description proceeds.

In the accompanying drawing forming a part of this specification,

Figure 1 is a longitudinal section of a spark plug embodying one form of the invention; Fig. 2 is a longitudinal section of a modified plug; Fig. 3 shows another modification of the plug, with a different shield.

In the form shown in Fig. 1, there is a conventional spark plug shell I0 provided with screw threads II adapting it to be screwed into the combustion chamber of an internal combustion motor. The shell-has a central bore I2 provided near its inner end with a shoulder I3 on which rests an insulating ring I4 of mica or the like. An electrode member I5 has its end I6 projecting into sparking relation with electrodes I! mounted in the shell.

A conductor I8 of any suitable construction makes electrical contact with electrode I5 and extends outward to a connection IS with a conductor carried by an insulating member 2I on the inner end of a shield 22 which is secured to shell I0 by a threaded collar 23. The outer end 24 of conductor 20 extends into channel 25 of the shield and may be connected in any suitable manner to a conductor running through the shield.

Within bore I2 and above ring I4 there is a sleeve 26 threaded onto electrode I5 and resting on ring I4. Around sleeve 26 and the lower end of conductor I8 there is compacted powder 21 which will be more fully described below.

Above the compacted powder 21 there is placed an insulating member 28, which may be of porcelain or other suitable material. This may be April 22, 1937, Serial No. 138,397

Canada May 16, 1936 held in place by any suitable means. In the form illustrated a flange 29 of the shell is bent over and holds in place a. washer 30 bearing upon the upper end of body 28. The parts are sufllciently held together by the compacted powder, but some means is desirable to prevent access of moisture to the compacted powder.

In the form shown in Fig. 2, many of the parts are identical, or substantially identical, with those shown in Fig. 1, and accordingly are given the same reference numerals and need not be separately described. The bore I2 oi the shell shown in Fig. 3 is somewhat enlarged at its upper end, providing a shoulder 3| in addition to the shoulder I3. Within this enlarged portion of the bore there is the lower end of an insulating member 32, which may be of porcelain or an equivalent material, and which extends upward to connection 33. The electrode I5 is shown with an integral enlargement 34 in place of sleeve 26, and compacted material 21' surrounds this enlargement of electrode I5 in the same manner as described above, and also surrounds and holds in position the lower end of insulating member 32. The upper end of the compacted powder 21 may be protected from moisture or the like by a washer 30 and inturned flange 29, similar to washer 30 and flange 29 described in connection with Fig. l.

A conductor I8 of any suitable construction extends from electrode I5 to connection 33. This conductor may be solid, hollow, or twopiece.

No shield is shown in Fig. 2, but it. will be understood that any suitable shield may be attached, as by threads 35.

In Fig. 3 there is shown a modification in which no porcelain insulator is used. The parts similar to those shown in Fig. 1 are designated by similar reference characters.

The bore I2" is made cylindrical above shoulder I3". A conductor 36 extends from central electrode I5 to connection 31. Around the outer end of conductor 36, and especially in-' sulating it from washer 30" and flange 29", there is an insulating sleeve 38 of mica or the like. Between flange 23 and connection 31 there are shown mica washers 39. A shield 40 with a lining 4| is shown screwed onto the shell H)" by threads The powder compacted at 21, 21, or 21" may be of the general type disclosed for sealing and holding purposes in my prior Patents Nos. 2,020,966 and 2,020,967, issued November 12, 1935. Mineral powder, that contains water of combination but is dry as to water of plasticity,

or free water, can in general be compacted by very heavy pressure to form a holding and sealing body; but lamellar crystalline mica and similar material which remains in scale-like particles, however finely ground, cannot be filled into and compacted uniformly in spaces like those commonly found in spark plugs, and therefore are not suitable for my purposes. Also, a material should be chosen which does not lose its water of combination at the temperature to which it is subjected in use.

Forming the powder into slip and spray-drying it into substantially spherical particles materially reduces the angle of repose and facilitates the ready and uniform filling of the powder into any space and consequently makes it feasible to compact the powder by high pressure in layers of suitable depth into a quite uniform material bonded throughout into a solid-gas-tight, slightly elastic body, having its particles in intimate holding contact with adjacent surfaces and with each other, so as to readily conduct heat.

In spray-drying the powder into spherical form, the fluidity of the slip, the manner of spraying, and the drying operation are so conducted that the surface tension of the liquid forms spherical drops of the sprayed slip, and retains these separated drops in substantially spherical form during the drying until the solid materials have been formed into substantially spherical shapes.

Where the material is to act as insulation, the basic compound should be chosen with regard to its inherent insulating character, and the resistance of such powder is greatly increased by treatment with a compound of the group consisting of boric acid and the borates of ammonium, magnesium, calcium, strontium and barium. Of these materials the borate of calcium is preferred as being very efficient and easily obtained. The borates of magnesium and barium are also quite effective and fairly easy to obtain. Strontium borate is not so readily available, and ammonium borate, while it has a distinctly beneficial effect, does not increase the dielectric to the extent that the other compounds mentioned will increase it.

A convenient way of treating the material with the boric compound is to dissolve the compound in the slip duringits preparation for spraydrying. Not only does the compound increase the dielectric of the material, but it also makes the dried particles smoother and harder so that the dried material has a smaller angle of repose and pours and packs more readily, and it also reduces the tendency the material may have to be hygroscopic.

As indicated above, the materials should also be chosen in view of the heat to which the insulation will be subjected in use. For use as insulation in spark plugs where a considerable degree of heat is encountered, it has been found that materials of the class of ground soapstone or brucite or kaolin are useable, these materials being mentioned as readily available examples and not as an exhaustive list.

Such materials, properly prepared, form excellent insulation for spark plugs and similar purposes. For example, powdered talc formed into a slip with about 1% of calcium borate, then sprayed into fine drops and dried into substantially spherical pellets, can be compacted into an insulating body that has a much higher dielectric than ordinary porcelain insulating material, and at the same time has a conductivity of heat of the order of that of iron or steel. Coupled with these qualities, it forms a gas-tight body and has sufllcient resiliency to maintain this gas-tight joint in spite of frequent and sharp alterations in temperature, even when in contact with metallic members having materially different co-eflicients of heat expansion.

It will be readily understood that, where insulation is to be employed in places not subjected to as high temperatures as spark plugs, there is a wider range of choice of basic insulating powder, since there are many insulating crystalline materials having water of crystallization and satisfactory compacting characteristics, but which begin to lose water of crystallization upon reaching the temperatures to which insulation is subjected in spark plugs.

While the construction of three forms of plug has been described and shown in some detail, it will be understood that many of the features may be modified without departing from the invention as set forth in the appended claims, the chief feature of the invention being, as to the spark plug, the employment of the compacted powder 21 to perform the three functions of sealing, holding the parts in proper relation, and constituting an insulator.

While the compacted powder may be employed for substantially the full length of the shell, as shown in Fig. 1, it is particularly advantageous at the inner end, where it is subjected to pressure of gases and to heat. At the outer end, which remains cooler, a body of any usual or suitable porcelain or the like may be used without incurring the leakage of gas or of electricity that is likely to result at the inner end of a spark plug in a high compression, high duty motor.

While the insulating material described was developed primarily for spark plugs and has peculiar advantages when used for that purpose, it may be employed for other uses where its qualities make it desirable, and therefore the broader of the appended claims directed to the insulating material are not confined beyond their stated terms to use in spark plugs or to material entirely suitable for such use. Substantially pure material is preferred, as generally having a higher dielectric, but some impurities are usually present in the commercial materials, and for many purposes considerable mixtures of less perfect insulating material is permissible.

The condition of the powder when compacted so that its grains interlock to form a good insulating gas-tight body gripping the adjacent parts and holding them in their desired relation, may be termed conglomerated, to distinguish from powder, such as most anhydrous rock powder, that remains separate particles in spite of any readily available amount of pressure, and from compaetible powder that is not subjected to the kind or degree of compacting that results in the described body of interlocked particles.

What I claim is:

1. A spark plug comprising a shell of conducting material, a central electrode, a body of compacted and conglomerated powder between the shell and electrode, having interlocking particles forming a gas-tight joint, holding the shell and electrode in their desired relative positions, and constituting, for at least a portion of the length of the shell, the sole insulation between the shell and electrode, and means protecting the ends of the body of compacted powder from moisture.

2. A spark plug comprising a shell of conducting material, a central electrode, and insulation between the shell and electrode, the outer portion of the insulation comprising a porcelain insulating body and the sole insulation between the electrode and shell near the inner end of said insulation consisting of compacted and conglomerated powder having interlocking particles forming a gas-tight joint and the conglomerated powder holding in the shell, electrode and porcelain material in their assembled relative positions.

3. A spark plug comprising a shell of conduct ing material, a central electrode, and a body compacted and conglomerated powder, consisting chiefly of magnesium silicate, between the shell and electrode, having interlocking particles forming a gas-tight joint, holding the shell and electrode in their desired relative positions, and constituting, for at least a portion of the length of the shell, the sole insulation between the shell and electrode.

4. A spark plug comprising a shell of conducting material, a central electrode, and insulation between the shell and electrode, the insulation, for at least a portion of its length, consisting of compacted and conglomerated powdered insulating crystalline material containing water of crystallization, that is not lost at the temperature to which it is subjected in use, and treated with a compound of the group consisting of boric acid and the borates of ammonium, magnesium, calcium, strontium and barium.

5. A spark plug comprising a shell of conducting material, a central electrode, and insulating material between the shell and electrode, the insulation, for at least a portion of its length, consisting of compacted and conglomerated magnesium silicate treated with calcium borate.

6. A spark plug comprising a shell of conducting material, a central electrode, and insulating material between the shell and electrode, the insulation, for at least a portion of its length, consisting of compacted and conglomerated spraydried pellets of magnesium silicate with a small amount of calcium borate.

'7. An insulating body consisting essentially of compacted insulating crystalline powder containing water of crystallization and treated with a compound of the group consisting of boric acid and the borates of ammonium, magnesium, calcium, strontium and barium.

8. An insulating body consisting of magnesium silicate treated with calcium borate.

9. A material for use in electric apparatus consisting of a powder formed of approximately spherical particles composed principally of insulating crystalline material containing water of crystallization and impregnated with a material of the group consisting of boric acid and the borates of ammonium, magnesium, strontium and barium.

10. A material in accordance with claim 9 and in which the principal ingredient is magnesium silicate.

11. A material in accordance with claim 9 and in which the principal ingredient is brucite.

12. A material in accordance with claim 9 and in which the principal ingredient is kaolin.

13. Electric insulation consisting of compacted pellets made by spray-drying a slip of magnesium silicate containing a small amount of calcium borate.

14. Insulating material consisting of spraydried pellets of magnesium silicate with a small amount of calcium borate.

15. The method of preparing material for use in electric apparatus which consists in forming a slip containing as its major ingredient finely ground crystalline insulating material containing,

water of crystallization, said slip also having dis solved therein a compound of the group consisting of boric acid and the borates of ammonium, magnesium, calcium, strontium and barium,

spraying said slip into separated drops under conditions which cause the drops to assume spherical form and drying the separated drops in approximately spherical form.

16. A method in accordance with claim 15 in which the principal ingredient of the slip is magnesium silicate.

17. A method in accordance with claim 15 and in which the principal ingredient of the slip is brucite.

18. A method in accordance with claim 15 in which the principal ingredient of the slip is kaolin.

19. A method of forming electric insulation which comprises forming a slip containing as its major ingredient finely ground crystalline insulating material containing water of crystallization, said slip also having dissolved therein a compound of the group consisting of boric acid and the borates of ammonium, magnesium, calcium, strontium and barium, spraying said slip into separated drops under conditions which cause the drops to assume spherical form, drying the separated drops in approximately spherical form, and compacting the spherical particles into a unitary gas-tight elastic mass having a high dielectric and high thermal conductivity.

O'I'IO C. ROHDE. 

